A single row deep groove radial ball bearing according to the present invention is used to support a rotary member such as a pulley and to removably support an offset load.
Automotive accessories such an alternator and a compressor are driven to rotate by an engine for driving a vehicle. Due to this, an endless belt is extended between follower pulleys fixed to end portions of rotating shafts of the automotive accessories and a drive pulley fixed to an end portion of a crankshaft of the driving engine, and the rotating shafts are constructed to be driven to rotate based on the circulation of the endless belt.
FIG. 5 illustrates the construction of a rotational driving portion of a rotating shaft 1 of a compressor constituting an automotive air conditioner. The rotating shaft is rotatably supported by rolling bearings, not shown, within a casing 2. A follower pulley 4 is rotatably supported around the circumference of a supporting tube portion 3 provided on an outer circumference of an end portion of the casing 2 by a single row deep groove radial ball bearing 5. The follower pulley 11 is formed into an annular configuration, on the whole, which has substantially a U-shaped cross section, and a solenoid 6 which is fixed to an end face of the casing 2 is disposed within an internal space of the follower pulley 4. On the other hand, a mounting bracket 7 is fixed to a portion protruding from the casing 2 at an end portion of the rotating shaft 1, and an annular plate 21 of a magnetic material is supported on the circumference of the mounting bracket 7 via a plate spring 8. The annular plate 21 is spaced away from the follower pulley 4, as shown in FIG. 5, when the solenoid 6 is not energized, while when the solenoid 6 is energized, the annular plate 21 is drawn toward the follower pulley 4 so as to be secured thereto, so that a rotational force is free to be transmitted from the follower pulley 4 to the rotating shaft 1.
With the rotational supporting device as described above, there maybe a case where a transverse central position (a chain line xcex1 in FIG. 5) of the endless belt wound around an outer circumference of the follower pulley 4 is not allowed to coincide with a transverse central position (a chain line xcex2 in FIG. 5) of the single row deep groove radial ball bearing 5. In such a case, a moment load in proportion to a deviating amount (offset amount) xcex4 between the transverse central positions of the two members is applied to the single row deep groove radial ball bearing 5 based on the tension of the endless belt. Then, a central axis of an inner ring 9 and a central axis of an outer ring 10 which constitute the single row deep groove radial ball bearing 5 do not coincide with each other (they are inclined).
With a mechanism like one as described above, when the central axes of the inner ring 9 and the outer ring 10 do not coincide with each other, there occurs an unbalanced wear of the endless belt which is wound around the outer circumference of the follower pulley 4, this making it difficult to secure the durability of the endless belt. In addition, the inclination of the central axes also makes it impossible to secure a certain gap between the annular plate 21 and the follower pulley 4, resulting in a possibility that these two members 21, 4 come into friction with each other. In the event that such a friction occurs, abnormal wear and abnormal noise are likely to be generated unfavorably. With a view to preventing the occurrence of these inconveniences, it is considered to reduce an angular gap of the single row deep groove radial ball bearing 5 in order to make it difficult that the central axes of the inner ring 9 and the outer ring 10 discord with each other.
Then, in order to reduce the angular gap for the aforesaid purpose, the following (1) to (4) procedures will be contrived.
(1) Radius of curvatures of cross-sectional shapes of an inner ring raceway 11 formed in an outer circumferential surface of the inner ring 9 and an outer ring raceway 12 formed in an inner circumferential surface of the outer ring 10 are made small (they are to be reduced so as to approximate 50% of the outside diameter of balls 13 constituting the single row deep groove radial ball bearing 5).
(2) As shown in FIG. 6, the raceway surface of one or both of an inner ring raceway 11a in an outer circumferential surface of an inner ring 9a and an outer ring raceway 12a in an inner circumferential surface of an outer ring 10a is formed into a combined surface, and rolling surfaces of balls 11 are brought into contact with both the raceway surfaces at three or four points.
(3) As shown in FIG. 7, the heights of shoulder portions 14a, 14b existing on transverse (in left and right directions in FIG. 7) sides of the raceway surface of one or both of an inner ring raceway 11b in an outer circumferential surface of an inner ring 9b and an outer ring raceway 12b in an inner circumferential surface of an outer ring 10b are made higher as indicated by a solid line than a general height indicated by a chain line in the same figure.
(4) As shown in FIG. 8, a plural row radial ball bearing 15 is used in which a plurality of balls 13, 13 are provided between a plurality of inner ring raceways 11c, 11c formed in an outer circumferential surface of an inner ring 9c and between a plurality of outer ring raceways 12c, 12c formed in an inner circumferential surface of an outer ring 10c, respectively.
The conventionally known and contrived constructions for reducing the angular gap as described above have the following problems.
First of all, in the case of the construction described under (1), although the angular gap can be reduced, the contact ellipses existing at abutting portions of the rolling surfaces of the respective balls and the inner ring raceway 11 and the outer ring raceway 12 become larger. Then, the contact ellipses dislodge from the inner ring raceway 11 and the outer ring raceway 12 when the central axes of the inner ring 9 and the outer ring 10 are only inclined slightly by virtue of a moment load. In this state, the rolling fatigue life of the rolling surface becomes extremely short. Thus, the construction described under (1) is not desirable as the allowable moment load becomes small. Note that while the configurations of the contact portions can be ellipse no more (resulting in a configuration in which part of the ellipse becomes lost) when the contact portions between the rolling surfaces and the raceway surfaces reach the transverse end edges of the raceway surfaces, for the purpose of description, a state like this will be referred to as xe2x80x9cthe contact ellipse dislodges from the raceway surfacexe2x80x9d in this specification.
Next, with the construction described under (2), the rolling surfaces of the balls 13 and the inner ring raceway 11a and the outer ring raceway 12a come to contact with each other at a plurality of contact positions, and moreover, in a state in which the engine is driven while the moment load is applied, since the contact positions become asymmetrical relative to the rotating axis of the ball 13, there occur much wear and heat based on slippage at the contact points, which is not desirable.
Next, with the construction described under (3), since the space between the shoulder portions 14a, 14a on the outer circumferential surface of the inner ring 9b and the shoulder portions 14b, 14b on the inner circumferential surface of the outer ring 10b becomes narrow, the diametrical thickness of a retainer 16 for holding the balls 13 becomes thin. Thus, as the thickness of the retainer 16 becomes thin, since it is difficult to secure the durability of the retainer 16, in consideration of the durability of the retainer 16, the effect of reducing the angular gap using the procedure described under (3) is limited.
Furthermore, with the construction described under (4), although the effect of reducing the angular gap and securement of the durability of the constituent components becomes compatible at a higher order, the increase in axial dimension cannot be avoided. The rotational supporting portion such as the follower pulley 4 has to be installed within a limited space in many cases, and therefore the increase in axial dimension is not desirable. Moreover, as the axial dimension increases, the production cost of the respective constituent components also increases.
It is an object of the present invention to provide a single row deep groove radial ball bearing which can solve the inconveniences as described above.
Similarly to single row deep groove radial ball bearings conventionally widely known, any of single row deep groove radial ball bearings according to the invention comprises an inner ring having a deep groove inner ring raceway formed in an outer circumferential surface thereof, an outer ring having a deep groove outer ring raceway formed in an inner circumferential surface thereof and a plurality of balls rotatably provided between the inner ring and the outer ring.
In particularly, in the single row deep groove radial ball bearing according to the present invention, at least one of the inner ring raceway and the outer ring raceway has a cross-sectional shape in which a transversely central portion thereof is different in a radius of curvature from transverse end portions between which the transversely central portion is interposed, and also transverse end edges of the portions having different radius of curvatures are made to be smoothly continuous with each other.
In the above-mentioned single row deep groove radial ball bearing as set forth in the invention, it is advantageous that the radius of curvature of the cross-sectional shape of at least one (or preferably, both) of the inner ring raceway and the outer ring raceway is made smaller at a transversely central portion and larger at transverse end portions, and transverse end edges of the portions having different radius of curvatures are made to be smoothly continuous with each other.
According to the single row deep groove radial ball bearings constructed as described above in accordance with the invention, the reduction of the angular gap and securement of the allowable moment load can be established at a higher order.
First of all, with the single row deep groove radial ball bearing as set forth in the invention, since the radius of curvature of the cross-sectional shape of the raceway is made larger at the transverse end portions, in the event that the central axis of the inner ring and the central axis of the outer ring are inclined toward each other based on the moment load, and that the contact point between the rolling surface of the ball and the raceway is displaced to the transverse end portion side of the raceway, the contact ellipse existing at the contact point becomes small. Due to this, it is difficult for the contact ellipse to dislodge from the raceway, the allowable moment load can be secured. Moreover, since the radius of curvature of the cross-sectional shape of the transversely central portion of the raceway is made smaller, when compared with a case where the entirety of the raceway constitutes a single curved surface having a large radius of curvature, the rolling surface of the ball and the raceway are allowed to get closer to each other to thereby reduce the angular gap.
Furthermore, in the above-mentioned single row deep groove radial ball bearing as set forth in the invention, it is advantageous that the radius of curvature of the cross-sectional shape of at least one (or preferably, both) of the inner ring raceway and the outer ring raceway is made larger at a transversely central portion and smaller at transverse end portions, and transverse end edges of the portions having different radius of curvatures are made to be smoothly continuous with each other.
According to the single row deep groove radial ball bearings constructed as described above in accordance with the other aspect of the invention, the reduction of the angular gap and securement of the allowable moment load can be established at a higher order.
With the single row deep groove radial ball bearing as set forth in the invention, since the radius of curvature of the cross-sectional shape of the raceway is made smaller at the transverse end portions, when compared with the single curved surface having a large radius of curvature, the rolling surface of the ball and the raceway are allowed to get closer to each other to thereby reduce the angular gap. In this case, too, since the radius of curvature of the cross-sectional shape of the raceway is made larger at the transversely central portion, even in the event that the central axis of the inner ring and the central axis of the outer ring are inclined toward each other based on the moment load, and that the contact point between the rolling surface of the ball and the raceway is displaced to the transverse end portions of the raceway, it is difficult for the contact ellipse to dislodge from the raceway to thereby secure the allowable moment load.